Green’s Dictionary of Slang

the brain, the head, knowledge.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Idea pot, the knowledge box, the head.
1796		Sporting Mag. July VIII 186/1: I am quite at a loss – But, good Lord! what signifies puzzling my idea-pot about it.
1811		Lex. Balatronicum [as cit. 1785].
1821		R. Waln Hermit in America on Visit to Phila. 2nd ser. 27: ‘Knowledge-box very small’ — ‘Idea-pot cursed empty!’.
1862		E. de la Bédollière Londres et les Anglais 315/1: idea pot, [...] la tête.
1873		Sl. Dict.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant I 480/1: Idea pot (thieves) the head; also called ‘knowledge-box.’.
1890–1904		Farmer & Henley Sl. and Its Analogues IV 1/1: Idea-pot (or -Box) subs. (old) . – The head.
1895		Crowe Aus. Sl. Dict. 37: Idea Pot, a man’s head.
1925		(con. 1899) H.P. Bailey Shanghaied Out of Frisco 53: The front of his idea-pot looks ez if a herd of mules had galloped over it!
1950		Goldin et al. DAUL 106/1: Idea-pot, the. The head; the mind.